1. Field of the Invention
The present invention relates to an improvement of a scan type digital X-ray imaging apparatus which has an X-ray detector capable of outputting digitalizable data or digital data upon receiving X-ray like a dental digital cephalometric X-ray imaging apparatus and wherein the X-ray slit beam scans an object to be examined while the X-ray slit beam emitted from the X-ray generator and the X-ray detector are synchronously moved in the same direction and an X-ray image of the object is produced.
2. Prior Art
Conventionally, an X-ray slit beam has scanned the head of the patient, which is an object to be examined, to obtain an X-ray image by a scan type digital X-ray imaging apparatus for medical use for example a dental cephalometric imaging apparatus disclosed in JP-A-7-143981. However, according to such an apparatus, when trying to make an image of a hard tissue such as a skull and a dental jaw bone clear by emitting a X-ray slit beam uniformly onto the head to be scanned, the images of a soft tissue such as skin and lips haven't been made clear. In contrast, the images of a hard tissue haven't been obtained when trying to make images of soft tissues clear by doing the same as mentioned above.
JP-A-7-8483 discloses an apparatus for solving the above-mentioned problems.
Namely the apparatus has a soft tissue filter, in which before an X-ray slit beam is radiated on the patient's head, a soft tissue filter which has a similar shape to a soft tissue area of a head is provided for a passage of the X-ray beam, thereby obtaining the image of the soft tissue. However, it has been difficult to adjust the position of the soft tissue filter on an actual soft tissue area of the patient's head so that accurate separation of the soft tissue area has been unable, further it has been required to prepare plural soft tissue filters depending on the size of the patient's head.
JP-A-5-252444 and JP-A-9-266901 propose a method wherein the data obtained by an X-ray detector is image processed to distinguish a hard tissue area and a soft tissue area and a gradation process is executed depending on the hardness of the tissue. However, such image processing has been complicated.
For example, according to the dental X-ray panoramic imaging apparatus as described in JP-A-8-19534, when an X-ray slit beam is radiated while rotating an X-ray generator and an X-ray detector opposing each other around the object, the rotational speed is controlled depending on the number of hard tissues existing on the passage of a beam, thereby obtaining the image of the hard tissue area even if plural bones are overlapped. However, in such a case, there has been no consideration on soft tissues and an X-ray slit beam have been rotatably radiated around the object unlike the dental digital cephalometric X-ray imaging apparatus wherein an X-ray slit beam scans the object.